The goal of this work is to describe the cellular mechanisms responsible for gastric HCl secretion. The research will follow two major approaches: (1) biochemical characterization transport events of membranes isolated from the oxyntic cell; and (2) analysis of the ultrastructural changes which accompany secretory activity. Membrane vesicles have been isolated from mammalian and amphibian stomach which we and others have shown to be largely derived from tubulovesicular and apical plasma membranes of the oxyntic cell, and which contain K ion-stimulated ATPase and H ion transport activities. We will study detailed kinetics of the K ion-ATPase, and the interrelationships between this enzyme and the H ion pump. Physiological activators of the vesicular H ion pump will be sought. Molecular modulation of the K ion-ATPase and H ion pump will be evaluated by group-specific modification, molecular extraction and substitution, and reconstitution studies. Morphological studies will define the ultrastructural detail of membrane migration, fusion and uptake associated with the "secretory cycle" of the oxyntic cell. Activators and inhibitors will be tested with a view toward differentiating secretory activity into two phases: membrane transformation and ion transport activity. Through ultrastructural analysis, the use of inhibitors and direct chemical analysis, the role of microtubules and microfilaments in oxyntic cell function will be examined.